Marcus Relationship Maintained During Ultrafast Electron Transfer Across a Supramolecular Capsular Wall.

Photoinduced electron transfer across an organic capsular wall between excited donors and ground-state acceptors is established to occur with rate constants varying in the range 0.32-4.0 × 1011 s-1 in aqueous buffer solution. The donor is encapsulated within an anionic supramolecular capsular host, and the cationic acceptor remains closer to the donor separated by the organic frame through Coulombic attraction. Such an arrangement results in electron transfer proceeding without diffusion. Free energy of the reaction (ΔG°) and the rate of electron transfer show Marcus relation with inversion. From the plot, λ and Vel were estimated to be 1.918 and 0.0058 eV, respectively. Given that the donor remains within the nonpolar solvent-free confined space, and there is not much change in the environment around the acceptor, the observed λ is believed to be because of "internal" reorganization rather than "solvent" reorganization. A similarity exists between the capsular assembly investigated here and glass and crystals at low temperature where the medium is rigid. The estimated electronic coupling (Vel) implies the existence of interaction between the donor and the acceptor through the capsular wall. Existence of such an interaction is also suggested by 1H NMR spectra. Results of this study suggest that molecules present within a confined space could be activated from outside. This provides an opportunity to probe the reactivity and dynamics of radical ions within an organic capsule.

Room-Temperature Phosphorescence from Encapsulated Pyrene Induced by Xenon.

Phosphorescence from pyrene especially at room temperature is uncommon. This emission was recorded utilizing a supramolecular organic host and the effect due to the heavy atom. Poor intersystem crossing from S1 to T1, small radiative rate constant from T1, and large rate constant for oxygen quenching hinder the phosphorescence of aromatic molecules at room temperature in solution. In this study, these limitations are overcome by encapsulating a pyrene molecule within a water-soluble capsule (octa acid, OA) and purging with xenon. While OA suppressed oxygen quenching, xenon enabled the intersystem crossing from S1 to T1 and radiative process from T1 to S0 through the well-known heavy atom effect. The close interaction facilitated between the pyrene and the heavy atom perturber xenon in the three-component supramolecular assembly (OA, pyrene, and xenon) resulted in phosphorescence from pyrene. Computational modeling and NMR studies supported the postulate that pyrene and more than one molecule of xenon are present within a confined space of the OA capsule.

Ultrafast trans → cis Photoisomerization Dynamics of Alkyl-Substituted Stilbenes in a Supramolecular Capsule.

Ultrafast spectroscopy reveals the effects of confinement on the excited-state photoisomerization dynamics for a series of alkyl-substituted trans-stilbenes encapsulated in the hydrophobic cavity of an aqueous supramolecular organic host-guest complex. Compared with the solvated compounds, encapsulated trans-stilbenes have broader excited-state absorption spectra, excited-state lifetimes that are 3-4 times longer, and photoisomerization quantum yields that are 1.7-6.5 times lower in the restricted environment. The organic capsule disrupts the equilibrium structure and restricts torsional rotation around the central C═C double bond in the excited state, which is an important motion for the relaxation of trans-stilbene from S1 to S0. The location and identity of alkyl substituents play a significant role in determining the excited-state dynamics and photoisomerization quantum yields by tuning the relative crowding inside the capsule. The results are discussed in terms of distortions of the ground- and excited-state potential energy surfaces, including the topology of the S1-S0 conical intersection.

Ultrafast Dynamics of Encapsulated Molecules Reveals New Insight on the Photoisomerization Mechanism for Azobenzenes.

Spatial confinement can have a profound impact on the dynamics of chemical reactions, especially for isomerization reactions that involve large-amplitude structural rearrangement of a molecule. This work uses ultrafast spectroscopy to probe the effects of confinement on trans → cis photoisomerization following ππ* excitation of 4-propyl stilbene and 4-propyl azobenzene encapsulated in a supramolecular host-guest complex. Transient absorption spectroscopy of the encapsulated azobenzene derivative reveals the formation of two distinct excited-state species with spectral signatures resembling the cis and trans isomers. Formation of the cis species indicates a direct excited-state isomerization channel that is not observed in cyclohexane solution. Comparison with the stilbene analogue suggests that this "hot" excited-state isomerization pathway for encapsulated azobenzene involves primarily in-plane inversion, whereas a 10-fold increase of the excited-state lifetime for the trans isomer suggests that crowding in the capsule hinders isomerization from the relaxed S1 geometry of the trans isomer. This work provides new mechanistic insight on the relative roles of inversion and rotation in the ultrafast photoisomerization of azobenzene derivatives.

Volume Conserving Geometric Isomerization of Encapsulated Azobenzenes in Ground and Excited States and as Radical Ion.

To probe the role of the supramolecular steric effects and free volume on photoreactions, geometric isomerization of neutral azobenzenes (ABs) and their radical ions, generated by electron transfer with gold nanoparticles, included within an octa acid capsule, was investigated. A comparison of the isomerization of ABs that proceed by volume conserving pyramidalization and stilbene analogues that proceed by volume demanding one bond flip has indicated the differing influence of 4-alkyl groups on these two processes.

Reversible Disassembly-Assembly of Octa Acid-Guest Capsule in Water Triggered by a Photochromic Process.

Octa acid (OA), a calixarene-based cavitand, forms a 1:2 capsular assembly with neutral 1,3,3-trimethyl-6'-nitrospiro[2H-1]benzopyran-2,2'-indoline and 1:1 cavitandplex with its open zwitterionic merocyanine form. Photochromic interconversion between the spiropyran and merocyanine leads to unprecedented reversible capsular disassembly and assembly. OA provides stability to the merocyanine in both the ground and excited states. The photochemically controlled disassembly and assembly process established here points toward the opportunity of using the OA capsule in delivering small molecules at the desired locations.

Effect of rate of induction of carbon dioxide anaesthesia on the time of onset of unconsciousness and convulsions.

The effect of different rates of induction of carbon dioxide anaesthesia on the time to loss of consciousness was investigated in broilers and hens. In experiment 1, 24 and 17 broilers, respectively, were exposed to 45 per cent carbon dioxide within 8 or 18 seconds (accession time). In experiment 2, 18 to 20 broilers and hens were exposed to either 35, 45, 55 or 65 per cent carbon dioxide within 8 seconds. The results indicated that, in general, the rate of accession is more critical than the final concentration of carbon dioxide; however, in 35 per cent carbon dioxide an exposure time of longer than 5 minutes is required to kill the birds. The time to sustained eye closure, time to onset of clonic and tonic convulsions and the duration of convulsive episodes were shorter in broilers than in hens. It is suggested that under commercial situations a final concentration of 55 per cent carbon dioxide would be suitable for killing broilers and hens.

Investigation into the batch stunning/killing of chickens using carbon dioxide or argon-induced hypoxia.

Three hundred and twenty broilers were stunned for 2 minutes in batches of 10 per crate in four treatments: 45 per cent carbon dioxide; 55 per cent carbon dioxide; 2 per cent oxygen, or 5 per cent oxygen presented as air diluted by argon. The number of survivors and the time to resumption of consciousness were recorded using the time to eye opening and response to comb pinching as indicators of consciousness. In 45 per cent and 55 per cent carbon dioxide and 2 per cent oxygen, 28, none and eight birds, respectively, survived out of 100 in each group. In 5 per cent oxygen the birds were still fully conscious after a 2 minute exposure period, and the test was discontinued. The time to recovery could be rapid after stunning in both the gases. It is suggested that a concentration of 55 per cent carbon dioxide or less than 1 per cent oxygen are required to kill broilers within a 2 minute exposure period, and that care should be taken to ensure that there is sufficient turbulence within the stunning chamber to avoid air pockets being trapped between the birds.

Effect of carbon dioxide stunning on somatosensory evoked potentials in hens.

The spontaneous electroencephalogram (EEG) and somatosensory evoked potentials (SEPs) were examined in 17 hens before and during stunning in 45 per cent carbon dioxide. The results indicated that EEG suppression and loss of SEPs occurred in 21 +/- 4 s and 30 +/- 2 s, respectively, after exposure to carbon dioxide, eventually leading to EEG silence in 101 +/- 18 s. Convulsions occurred 15 seconds after the loss of SEPs, suggesting that the hens convulsed while they were unconscious. It is concluded that the induction of anaesthesia can be rapid in carbon dioxide stunning and in this respect carbon dioxide is potentially suitable for stunning poultry under commercial conditions.

Effect of mixing male sex types of cattle on their meat quality and stress-related parameters.

Mixing of male cattle prior to slaughter results in increased physical activity, particularly homosexual behaviour, teasing and mounting. The number of mounts exhibited during the initial 4 h after mixing showed statistically significant correlations with serum enzyme levels at slaughter, pHu, glycolytic metabolites, colour and pigment proportions of M. longissumus dorsi at 48 h post-mortem. The amount of teasing showed significant correlations with pHu, glycolytic metabolites, colour and pigment proportions. The aggressive behaviour, pushing and butting, occurred only as retaliative acts and did not seem to affect meat quality. Among the male types used in this study, the vasectomised bulls were found to be more homosexually hyperactive and thus produced the highest number of dark-cutting carcasses, suggesting that the vasectomised bulls are more prone to dark-cutting due to mounting that occurs during pre-slaughter mixing.

Efficiency of bleeding of broilers after gaseous or electrical stunning.

The efficiency of bleeding of broilers (g blood/kg liveweight) was measured after stunning them with either 45 per cent carbon dioxide in air for two minutes or with 2 per cent oxygen (achieved by displacing air with argon) for two minutes or with an electric current (77 or 104 mA at 50 Hz for four seconds). The results indicated that the initial rate of bleeding was higher in the electrically stunned broilers with non-fibrillated hearts than in the gas stunned broilers and electrically stunned broilers with fibrillated hearts. This difference was significant up to 60 seconds after neck cutting (P less than 0.05) but after 140 seconds all the broilers had bled out to a similar extent (30 to 33 g/kg liveweight). It is concluded that after gas stunning the time interval between neck cutting and scalding should be 60 to 140 seconds.

Preferential feeding behaviour of hens in different gaseous atmospheres.

1. The object of this study was to identify the concentrations of carbon dioxide (CO2) and hypoxia (induced by argon) which hens could detect and by preference avoid. 2. Hens were housed in an apparatus consisting of an upper roosting chamber connected to two descending passages which led to separate identical feeding chambers. The gas concentration in both these feeding chambers could be regulated. 3. The hens were allowed to feed in either a normal air atmosphere or an altered atmosphere containing a sub-stunning concentration of CO2 or argon. The birds' preference for feeding in the two chambers was used as an indicator of the concentration which they chose to avoid. 4. The study involved two experiments. In the first it was found that when the concentration of CO2 was raised above 5%, or the concentration of oxygen was reduced to 10% or below, the occupancy of that chamber was significantly reduced. 5. The results of the second experiment confirmed that a concentration of above 7.5% CO2 or oxygen levels of 10% or below can be detectable to hens and, given a free choice, the hens learnt to avoid such atmospheres. 6. The presence of a dominant bird in the roosting chamber or in the feeding chamber containing air caused the subordinate birds to enter the treatment chamber containing gas. This would imply that the unpleasantness of the stunning gases at the concentrations used in this study was less severe than the social pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the somatosensory evoked potentials and spontaneous electroencephalogram of hens during stunning with a carbon dioxide and argon mixture.

A previous investigation indicated that when hens were exposed to 2% oxygen in argon (anoxia) EEG suppression and loss of SEPs occurred at 17 and 29 s after exposure. In this study, hens were exposed to 49% carbon dioxide in air (hypercapnic hypoxia) or 31% carbon dioxide with 2% oxygen in argon (hypercapnic anoxia) and their spontaneous electroencephalogram (EEG) and somatosensory evoked potentials (SEPs) were investigated. The results indicated that EEG suppression and loss of SEPs occurred in 11 and 26 s, respectively, in hypercapnic hypoxia. These events occurred at 11 and 19 s, respectively, after exposure to hypercapnic anoxia. These results indicated that, with regard to preslaughter stunning/killing of chickens, a mixture of 31% carbon dioxide with 2% oxygen in argon resulted in a more rapid loss of evoked responses in the brain when compared with 49% carbon dioxide in air or with 2% oxygen in argon. It is concluded that stunning chickens with low concentrations of carbon dioxide in argon would result in a more rapid loss of consciousness.